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MRA
Argelander Fellow, University of Bonn

M. Reza Ayromlou
Computational Astrophysicist

I study how galaxies form and evolve by following their gas, from galaxies out to the cosmic web.

Research Publications
Four questions
Research

Follow the baryons

Four questions run through my work. Each opens a chapter of my research page, with the findings, figures and papers behind it.

Feedback and the open baryon cycle

Where are the missing baryons?

Beyond the halos. Black holes and supernovae push gas past the virial radius, out to the closure radius, a scale I introduced, and into the intergalactic medium. Today fewer than 30% of all baryons sit inside galaxy-hosting halos, against about 45% of the dark matter.

Where the baryons are, with gravity alone and with feedback Schematic of four halos on the cosmic web, with 100 dots standing for all the baryons in the Universe. With gravity alone, 45 of them sit inside halos, as 45% of the dark matter does. With feedback, 16 are pushed beyond the halo boundaries, out toward the closure radius, and fewer than 30 remain inside. virial radius closure radius
Baryons in halos Between halos Pushed out by feedback Dark matter Schematic: each dot is 1% of all baryons. The fractions are from the TNG, EAGLE and SIMBA simulations.

Dark matter in halos 45%

Baryons in halos 45%< 30%

Read the chapter Ayromlou et al. 2026
Environment, stripping and conformity

How does the neighborhood switch galaxies off?

≥ 5 Mpc the reach of galactic conformity, over 16 million light-years Ram-pressure stripping should begin before satellites even cross the halo boundary, and neighbors share the star-forming state of their central galaxy out to at least 5 megaparsecs, in models and in SDSS and DESI data. Read the chapter Models across techniques

Do different models build the same galaxies?

≈ 3× apart in the stellar mass at which galaxies stop forming stars Matched galaxy by galaxy on the same dark-matter merger trees, L-Galaxies and IllustrisTNG agree on stellar masses, but IllustrisTNG switches galaxies off at stellar masses about three times lower. Read the chapter The early Universe

Can our models make the galaxies JWST sees?

up to 100× more massive early galaxies than in the previous model Not yet, but closer: when star formation and feedback depend on the local gas density, massive UV-bright and quenched galaxies in the first two billion years become up to a hundred times more abundant. Read the chapter
Publications

Latest papers

All 33 publications
News

News

  1. October 2026

    PROFI is now public

    PROFI, my code for radial profiles of density, velocity, temperature, entropy and more in cosmological simulations, is now open source on GitHub under the MIT license.

  2. October 2026

    CENSAT is now public

    CENSAT, which identifies central and satellite galaxies in both simulations and observations, is now open source on GitHub under the MIT license.

  3. 2026

    iCluster awarded ~20 million CPU hours

    The iCluster simulation project was awarded about 20 million CPU hours on the LRZ supercomputer.

  4. 2026

    iCluster simulations complete

    The full iCluster simulation suite has finished running, and analysis is now underway.

Mohammadreza (Reza) Ayromlou About me

Galaxies, clusters,
and the gas between.

I am the Argelander Fellow at the University of Bonn, based in Bonn, Germany. Before Bonn I was a postdoctoral researcher at the Center for Astronomy of Heidelberg University, following a bridging postdoc at the Max Planck Institute for Astrophysics, where I completed my PhD in 2021 together with LMU Munich.

I develop and analyze cosmological simulations to understand how cosmic structures and galaxies form and evolve.

More about me CV
papers, published and submitted
33
as first author
7
led by students I supervise
4
Patzer Prize, for introducing the closure radius
2023
Get in touch

Interested in the code, simulations, or data?

If you would like to use my code, run with the simulations, or work with the data behind any of these papers, feel free to reach out — I am always happy to have a conversation.

Public data and code

Get in touch For students